I generally find it hard to trust people on a day to day basis. I always think there's an ulterior motive.
Why don't I trust easily? I don't know, I just don't. With that being the case, there are just some persons who beg not to be trusted.
For example, one signs up to a social network (like Facebook) and proceed to knowingly, complete the form with misleading data. Why would someone do that? Especially seeing that outside of username and password, most of this data is optional!!!! So instead of just leaving the fields blank (to protect their privacy), they put in faulty data and mislead the "public" in a bid to protect their privacy.